The power went back on at Hartsfield-Jackson Atlanta International around midnight last night after a fire in an underground faclity knocked out power airport-wide around 1 p.m. Eastern time on Sunday afternoon.

On Sunday all operations at the airport ground to a halt with thousands of passenger stuck inside the terminal into darkness and on planes.

Delta alone canceled more than 1,000 fllights and hundreds of other had to be diverted or held on the ground at their departure cities. At least 300 Delta flights are already canceled for today.

Most of the 300 Delta cancellations Monday are early morning, inbound flights to ATL to give the operation there an opportunity to more quickly rebound. Delta’s flight schedule in ATL is expected to return to normal by Monday afternoon.

Another winter storm – named Nemo – is on the way and airlines are getting ready for it by issuing weather-related fee waivers and encouraging travelers to change their flight dates, postpone travel or re-route their trips to and from a long list of cities in the northeast.

If I could fly somewhere this weekend, I’d choose Iceland for the chance to see for myself what that volcano is doing. But since the ash has caused the worst disruption in air travel since 9/11, that’s not going to happen.

But if I could fly anywhere in the United States this weekend, I’d choose Denver.

There’s no volcano erupting there, but this weekend the city is hosting Doors Open Denver – a free event that offers a look inside dozens of buildings around town that are usually closed to the public. My column on msnbc.com this week, Welcome! The Door is open, includes a run-down of half a dozen cities that host this sort of event, but here’s a preview, along with some photos that didn’t make it into the posted story.

Billed as a celebration of the city’s built environment and design, the 6th annual Doors Open Denver takes place April 17-18 and includes 80 to 90 buildings around town that are usually off-limits to the public. This year’s theme is adaptive re-use so you’ll get to see many old buildings being used in creative new ways.

This year, participating sites include the city’s old main post office, which has been turned into a high-security federal courthouse; a restored mansion that serves as the Colorado Governor’s Residence; a theater in a former mortuary; a Yellow Cab garage that now houses businesses and residential units; and the Historic Sugar Building, which was built in 1906 as the headquarters for the Great Western Sugar Company and now houses office and retail space, and two original Otis cage elevators.

One sure-to-be-popular site is the Daniels & Fisher Tower, which was once the tallest building in Denver. The Italian Renaissance Tower has a restored lobby with marble floors and walls and a 17th floor boasting a giant clock-face and a balcony that offers great 360-degree views of the city, the surrounding plains and the mountains.

(Courtesy: Gregory Thow)

More doors openedIf you can’t make it to Denver this weekend, don’t worry. Doors at many other usually off-limits locations will soon be opening in cities throughout North America, including Toronto, New York, Chicago, and in Lowell, Mass.

May 13-15 are the dates for the 9th annual Doors Open Lowell event, which will feature everything from reclaimed and restored mill buildings to a 1920’s classical revival Masonic Temple with curious chambers and meeting rooms, and the subterranean space that once housed giant turbines for a power plant that ran a local mill.

During Doors Open Toronto, held on May 29-30, 150 buildings of architectural, historic, cultural and/or social significance will be open to the public. Highlights include: Toronto’s City Hall, which offers self-guided tours of the Rotunda, the Council Chambers and the Observation Deck, and the five-story red brick Toronto Flatiron Building, which pre-dates New York City’s famous Flatiron building by about ten years. Also open to the public will be the Canada Life building, which has a weather beacon and a 17th floor tower room offering a panoramic view of downtown Toronto and Lake Ontario, as well as the restored circa-1920 Canon Theater — once the largest and most elegant vaudeville and motion picture palace in Canada.

Mark your calendars: New York hosts Open House New York on Oct. 9-10, with more than 200 sites participating throughout all five city boroughs, including the Woolworth Building, Radio City Music Hall and the Atlantic Avenue Tunnel, which is accessed not by a door, but by a manhole.

If you’re still trying to figure out whether or not you’re going to take that scheduled trip to Mexico, one of the variables is certainly the policy set forth by your airline. Will they refund your ticket price? Waive the change fee? Allow you to go Montreal instead of Mexico City?During the initial flu-frenzy, many airlines set and then revised their policies, in most cases extending the dates during which they’d waive change fees.

If changing destination, travel must originate within 14 days of original departure date. US Airways has revised its policy and now allows departure after 14 days from original departure date but does not specify when alternate travel must be completed by (most likely within one year of original departure).